This invention relates to radiation-emitting panels of the kind having two parallel plates sealed with one another around their edges and enclosing a gas-discharge volume at reduced pressure, at least one of the plates being transparent to the radiation.
In many applications, it is desired to be able to produce even illumination over a large area, such as when back lighting instruments. Preferably, the illumination is of high intensity with a low power and heat dissipation while being compact and of light weight.
Fluorescent lighting, in which light is generated by photo-ionization of a phosphor layer in a gas-discharge tube, is ideally suited to this, as far as the level of illumination and power dissipation is concerned. Where even illumination is required over a large area, however, it is necessary either to use several fluorescent tubes in parallel with one another or to use a tube that is bent, in an attempt to produce an even distribution of light. In WO 87/04562 there is described a display in which an arrangement of parallel tubes is reproduced in a flat panel by means of walls that divide the panel into separate discharge paths, each having its own electrode. A bent tube arrangement is similarly reproduced by walls defining a circuitous path between two electrodes. It is usually also necessary to use some form of diffuser in front of such arrangements to produce a more even illumination. This does still not produce illumination which is distributed sufficiently evenly for some applications because of the presence of the walls.
WO 87/04562 also describes a flat panel fluorescent device formed by two glass plates coated with phosphor on their facing surfaces. The plates are spaced from one another and sealed around their edges, the space between the plates being evacuated to a low pressure. Electrodes extend along opposite edges inside the space between the plates, so that discharge can be produced between them. The problem with this construction is that, because of the reduced pressure within the device the plates must be relatively thick to be able to withstand the pressure differential across them. This leads to a device which is relatively heavy and bulky.
It is an object of the present invention to provide a radiation-emitting panel which can be used to avoid these disadvantages.